Handcuffs! In David Mackenzie’s Tonight You’re Mine, the American rock star Adam (Luke Treadaway) gets into a fight with Morello (Natalia Tena), who fronts her own Brit girl band, at the T in the Park music festival in Kinross, Scotland. A black preacher shows up, cuffs the squabblers together and speeds away. Until they can be freed, the two are sentenced to each other’s reluctant, rancorous company. Guess what happens? Actually, don’t bother guessing. You already know.

I’ll bet that in Alfred Hitchcock’s The 39 Steps, when a man on the run (also in Scotland) was manacled to a beautiful blond who thinks he’s a killer, knowledgeable viewers groaned, “Not the old handcuff routine again!” And that was 1935. You’d have thought this meet-cute cliché would have been forcibly retired by now, but it stills shows up — last December, for instance, in an episode of the ABC sleuth drama Castle. At least Richard Castle and his luscious cop partner Kate Beckett didn’t stay cuffed for the whole episode, as Adam and Morello do here for almost all of Tonight‘s 80-minute running time. Apparently nobody has a smart phone, on which dozens of YouTube videos on handcuff lock-picking can be summoned in a few seconds. And though Adam and Morello are often on stage in front of 85,000 fans, neither thinks to ask the crowd, “Can anyone help us get these things off?”

Thomas Leveritt, the novelist credited as screenwriter for this largely improvised, fitfully ingratiating film, might say that, in virtually every movie romance, the lovers-to-be are metaphorically chained together. Since there’s little dramatic tension in a couple falling in love at first sight and sailing serenely through life, the standard romantic comedy has a plot synopsizable in 10 words: “I hate you.” (One movie hour later:) “I love you.” The man and the woman must overcome their initial antagonism by being forced to suffer each other’s company, because… because he got her pregnant (Knocked Up). Because he paid her to be with him (Pretty Woman). Because he’s a newspaperman and she’s the story (It Happened One Night, Roman Holiday). Because he’s rich and she’s after his money (The Lady Eve). Because they have to pretend to be lovers (The Proposal). Or because they’re handcuffed at a rock festival. Call it a dry run for the mutual indenture of marriage.

The movie’s subsidiary characters are chained only to their stereotypes. Morello’s boyfriend (Alistair Mackenzie, the director’s brother) is a staid banker; Adam’s girlfriend (Ruta Gedmintas) is a blonde supermodel he met in rehab. Glancing at Adam’s new ball-and-chain — actually chain-and-ball, since the sex comes later — she says, “Call me when you’re single,” and stalks off. The banker and the blonde are of use primarily in a scene where each of the two couples awkwardly tries to cuddle when they bed down; after that the superfluous parties are instantly disposable. The other possible romantic pairing involves Adam’s nerdish band mate Tyko (Matthew Baynton) and Morello’s luscious cohort Kirsty (Kari Corbett), who also start out hostile. When Tyko hears that name of the girls’ band is The Dirty Pinks, he snorts, “Why don’t you just call yourselves The Vaginas?” By the rules of movie romance, he and Kirsty should also be destined to spend an awful, beautiful night finding love, but she has other arms to fall into.

This is light stuff for David Mackenzie. His 2003 feature Young Adam ignited sparks of sexual heat among Ewan McGregor, Tilda Swinton and Emily Mortimer; his recent Perfect Sense imagined the end of humanity as a deaf-blind grope toward love by McGregor and Eva Green. Tonight You’re Mine has the feel of a movie by Michael Winterbottom, the prolific Brit director who often mixes fiction and documentary (Welcome to Sarajevo, In This World, Tristram Shandy, The Trip). This one is closest to Winterbottom’s 9 Songs, which alternated scenes from a love affair with performances by rock groups — except that 9 Songs featured explicit sex scenes. The erotic tussle in Tonight You’re Mine is mild in comparison with the Winterbottom film or the earlier Mackenzies; it’s just a mostly clothed frolic in the shower for Adam and Morello.

If the film is to work at all — and it eventually does — the two 27-year-old leads must radiate enough star quality to obviate the ramshackle plot. They just about do. Treadaway, from British TV series (Innocent, Mist: Sheepdog Tales) and supporting roles in movies (Attack the Block, Clash of the Titans), has a rock star’s willowy frame and watchful hauteur; he also persuasively counterfeits an American accent. Tena made a sweet early impression a decade ago as the schoolgirl Hugh Grant’s young charge had a crush on in About a Boy. In 2004 I named her Best New Face for her captivating performance in the off-West End play Gone to Earth. There, and as Osha the wildling woman in Game of Thrones, Tena exuded the feral musk of a creature the world can try to cage but will never tame. Her Morello is a lesser but still willful soul in chains, whom the actress humanizes with her throaty voice and intense line readings.

Filmed in five days at the 2010 T in the Park festival, this vibe movie counts on doc footage of the revelers to accelerate the slow pulse of its main story. In the U.K., Tonight You’re Mine was released as You Instead, both being names of songs Adam performs. The U.S. distributor might be hoping that boomers would take the new title for a reference to the old Shirelles hit “Will You Love Me Tomorrow.” Not so, but most of the music included in the film sounds like ’60s spirit. Newton Faulkner’s rendition of his 2007 hit “Gone in the Morning” plays like a lost Joe Cocker clip from Woodstock. Morello and Adam’s share their first moment of public intimacy when he must join The Dirty Pinks for “Tainted Love,” a 1964 number covered by everyone from Soft Cell to Marilyn Manson and Rihanna.

At its best, this modern movie has the feel of a half-century-old rave-up. As for the plot, it must date back to the Iron Age. Someone in 1200 B.C. probably took that new gadget, handcuffs, slipped them on the wrists of two young savages and thought, “Awww, aren’t they cute?”